Method of producing direct positive photographs having increased density



. R. E. STAUFFER 2,497,917. METHOD OF PRODUCING DIRECT POSITIVEPHOTOGRAPHS Feb. 21, 1950 HAVING INCREASED DENSITY Filed Oct. 17, 1947FIG. 2.

INVENTOR ATTORNEYS RQBFERT ESTAUFFER Patented Feb. 21, 1950 UNITED STATEMETHOD OF PRODUCING DIRECT POSI- TIVE PHOTOGRAPHS GREASE!) DENSITYHAVING IN- Robert Eliot Stauffer, Rochester, N. Y., assignor to EastmanKodak Company, Rochester, N. Y., a corporation of New Jersey ApplicationOctober 1'7, 1947, Serial No. 780,569 4 Claims. (01. 9588) Thisinvention relates to photography and particularly to a method of makingdirect positive photographs.

Direct positive effects may be produced by solarizing the developablelatent image by overexposure, by using a second exposure to obtain theSabattier or the Clayden effect or by redeveloping a developed negativeimage. Solarizable sensitized products require very intense exposures toobtain the desired direct positive photograph. The use of a secondexposure has obvious disadvantages from the point of view of practicaltechnique. Redevelopment adds at least two operations to the usual andnormal developing procedure.

Fallesen U. S. patent application, Serial No. 780,405, filedconcurrently herewith describes forming a direct positive image in asuitable silver halide emulsion by exposing the emulsion in the usualway and developing it in a developer which is capable of giving aerialfog. The emulsion is preferably of the internal latent image type suchas described in Davey and Knott U. S. patent application, Serial No.790,232, filed December 6, 1947, now abandoned.

I have discovered that certain compounds which have been used asphotographic antifoggants or emulsion addenda may be added to thedevelopers used in the process of Fallesen patent application, SerialNo. 780,405, and that increased aerial fog, that is, higher maximumdensity of the reversal image, results from this use of the compound.The compounds which I propose to use are heterocyclicnitrogen-containing ring compounds having 5 or 6 atoms in theheterocyclic ring and so constituted as to increase the maximum densityof the positive image obtained in developing solutions capable ofproducing aerial fog.

I have found that in the development of certain emulsions, such as the"internal latent image emulsions, the use of certain anti-foggants orother compounds in the developing solutions increases the density. inthe unexposed areas by intensifying the aerial fog in the low exposureregions, At the same time, the ordinary anti-foggant property isexhibited in the toe portion of the reversal curves, that is, the areasof maximum exposure. I believe that this enhancement of aerialfog inunexposed areas is a new phenomenonwhich. offers considerable value fordirect positive photographic materials.

In the accompanying drawing, the two figures res a a eri iis ve ei ho gtnh mu.-

sions illustrating results obtained according to my invention.

The photographic emulsion used in the process of my invention is agelatino-silver halide emulsion such as a silver bromide emulsion, asilver bromoiodide emulsion, or a silver chloro-iodide emulsion. It neednot contain optical sensitizing dyes, although certain sensitizing dyesmay be added to it for the purpose of inducing aerial fog, as explainedmore fully in Fallesen application, Serial No. 780,405. A suitableemulsion is that known as Burtons emulsion, described in Wall,Photographic Emulsions, 1929, pages 52 and 53. Burtons emulsion is madeasfollows:

A. Silver nitrate grams 100 Water cubic centimeters 500" Ammonia-to formclear solution 7 l B. Potassium bromide grams '80 Potassium iodide do 50Soft gelatin do 20 Water cubic centimeters 1000 0. Dry gelatin grams 250B is heated to C. and A, cold, added to B with constant shaking,digested for 20 minutes at 50 C., and allowed to cool slowly. C is addedafter being allowed to swell for 20 minutes in water, drained, andmelted. The emulsion is then set and washed.

An internal latent image emulsion, that is, one which forms the latentimage mostly inside the silver halide grains, as described on pages 296and 297 of Mees, The Theory of the Photographic Process, 1942, isespeciallyuseful for the process of my invention.

Most of the internal latent image emulsions are silver bromo-iodideemulsions of high iodide content, preferably containing at least 10%-20% of iodide. Burtons emulsion is an emulsion of this type, having asilver iodide contentof approximately 40% of the content of silverhalide. It is not absolutely essential, however, for the emulsion .tocontain silver iodide.

An internal latent image emulsion made as.

described in Davey and Knott U, S. application,

Serial No. 790,232, filed December 6, 194,7, may, also be used accordingto my invention. This.-

emulsion is prepared by first forming in the ab-. sence of ammonia andin one or more stages silver salt grains consisting at least partly of asilver salt which is more soluble in water than silver bromide,subsequently converting the grainsto silver bromide or silverbromoiodide, and if thesilver iodide content of the emulsion is lessthan 6% ira a d .0 et il swarms .i a nssrse.

Solution No. l:

Inert gelatine... 20 grams KC] 20 grams at 40 0. Water 560 cubiccentimeters sow ng; No. 2: 100

grams Water. 520 cubic centimeters} 45 Solutio rgo. 3: 195

l 3 grams Q w ater 520 cubic ccntimeters} 45 Solution No. 4:

KBr l... 160 grams Kl .l. 40 grams }at 45 0. Water 500 cubic centimetersRun Solutions Nos. 2 and 3 simultaneously into Solution No. l in avessel, taking 90 seconds to do this. Then ripen for 1 minute at 45 C.Next add Solution No. 4 then ripen for 20 minutes at 45 C. Next add 235grams of inert gelatine (dry). Then ripen at 45 C. for 15 minutes duringwhich time the gelatine dissolves. Set and shred the emulsion and thenwash until free from all soluble bromide and then add about 150 cc. of10% solution of KCl (by weight), and then add water to make 3 /2 liters.

An internal latent image type of silver halide emulsion may be definedas one which, when a test portion is exposed to a light intensity scalefor a fixed time between /100 and 1 second, and

developed for 4 minutes at 20 C. in the ordinary,

surface developer (Example 1), exhibits a maximum density not greaterthan /5 the maximum density obtained when the same emulsion is equallyexposed and developed for 3 minutes at 20 C. in an internal typedeveloper (Example 2). Preferably the maximum density obtained with thesurface developer is not greater than fn' the maximum density obtainedwhen the same emulsion is developed in the internal type developer.Stated conversely, an internal latent image emulsion, when developed inan "internal type developer (Example 2) exhibits a maximum density atleast 5, and preferably at least 10, times the maximum density obtainedwhen the same emulsion is exposed in the same way and developed in asurface developer (Example 1).

The developer used in the method of my invention should be one whichproduces oxidation fog or aerial fog. Such developers have beendescribed by Dundon and Crabtree in American Photography, 1924, vol. 18,page 742. An example of such a developer is a hydroquinone developercontaining little or no sulfite, and is illustrated in Example 3.

The aerial fog may be produced in the developer in various ways and maybe accelerated or intensified by resorting to various expedients. Thedeveloper used should preferably have low sulfite ion content and shouldpreferably contain no silver halide solvent more powerful (as a silverhalide solvent) than sulfite. Aerial fog may also be increased bybubbling air vigorously through the developer in such manner that theair comes frequently into contact with the emulsion surface of thephotograph during development. Certain chemical agents such as coppersulfate incorporated either in the developer or in the emulsion itselfmay be used to produce or encourage the production of aerial fog.Hydrogen Amount per Compound liter of developer Grams Benzotriazole 0. 4Methyl benzoti'iazole l 0. 05-0. 2 Ethyl bcnzotriazole 0. 05-0. ll-Ethyl oxiudole. 0.10 5-Nitroindazole. 05-0. 1 (i-Nitrobenzimiclazole0. 050. 1 Histidinc 0. 10-0. 2 Ethyl benzo. :azole O. 10 N-etliylpyrrole 0. 1-0. 2 2,5Dimethylpyrrole 0. 05-0. 22,4Dimethyl-fi-carbcthoxypyrrole. 0. 05-0. 2 2,3-Dirncthyl quinoxaline.0.050. 10 2-Thio'2,4(3,5)-thiazolediono 0. 050. 202,4,6-Tri-isopropylamino-S-triozi 0. l(). 22,4-Dimethylamino-(i-chloro-S-triazine.. 0. l-0. 2 2,4-Di-(B-mcthoxyethylamino)-6-chloro-S-triazinc. 0. 22,4,G-Tri-u-butylamino-S-triazine 0. 2l-Garboxymcthyl-3-phenyl-2-thiohydantoin 0. l-0. 5l,4-diphcnyl-3-anilino-5-phenylimiuo.

l,2,4triazoline 0.05 to 0.50

An ordinary surface type developer, that is, one which develops an imageonly on the surface of the grains of internal latent image emulsions, isthe following:

Example 1 p-Hydroxyphenylglycine "grams" '10 Sodium carbonate (crystals)sdo Water to liter 1 Development time, 4 min. at 20 C.

An internal type developer, that is, one which develops an image insidethe grains of an internal latent image emulsion is the following:

Development time, 3 min. at 20 C.

My invention will be described by reference to the following specificexamples.

Example 3 An emulsion such as the Davey and Knott emulsion describedabove was coated on a support, dried, and exposed on an Eastman IIBSensitometer (Journal Society Motion Picture Engineers, 17, 1931, page536). The exposed emulsion was then developed for 12 minutes at 68 F. inthe following developing solution:

Hydroquinone grams 22.5 Sodium sulfite do 30 p-Formaldehyde do 7.5Potassium metabisulfite do 2.6 Boric acid crystals do 7.5 Potassiumbromide do 1.6 Water to liter 1 The developer was agitated during thedevelopment by forcing air through a sintered glass bubble tubecompletely submerged in the developer tank. A similar emulsion exposedin the same way was developed for the same length of time in the samesolution containing 0.4 g. of benzotriazole per liter of developingsolution. Direct positive images were obtained in each case and wereplotted as shown in Fig. 1 of the accompanying drawing. Curve A wasobtained from the developer containing no benzotriazole and curve B wasobtained from the developer containing benzotriazole. The curves showthat a higher maximum density was obtained with the developer containingbenzotriazole.

Example 4 The same emulsion as that used in Example 3 was exposed in thesame way and portions were developed in a developer of the followingcomposition:

Water to 1 liter containing 0, 0.05, 0.1 and 0.4 g. ofmethylbenzotriazole per liter of developing solution. Sensitometriccurves were obtained from these exposures as shown in Fig. 2 and thesedisplay the effect of a range of concentrations of anti-foggant. Curve Awas obtained from the development containing no anti-foggant, curve Bfrom the development containing 0.05 gm. per liter of methylbenzotriazole, curve C from the development containing 0.1 gm. per literof methyl henzotriazole and curve D from the development containing 0.4gm. per liter of methylbenzotriazole. These curves show that atconcentrations of from 0.05 to 0.1 gm. of. methyl benzotriazole perliter of developer, the maximum density and gamma are increased, but athigher concentrations, maximum density and gamma are decreased and at aconcentration of 0.4 gm. per liter, they are lower than they were withthe developer containing no methylbenzotriazole.

Example Additional strips of the film used in Example 3 were exposed inthe same way and developed in the developer of Example 4, with variousconcentrations of G-nitro-benzimidazole nitrate added to the developer.The development then was 5 minutes and the developer was aerated as inExamples 3 and 4. The concentration of the order of 0.05 g. per liter ofdeveloper G-nitrobenzimidazole nitrate was found to be effective inincreasing maximum density and decreasing minimum density. At higherconcentrations maximum density was decreased although at a concentrationof 0.1 g. per liter of developer, the maximum density was higher and theminimum density lower than in the case of the developer containing noanti-foggant. The table indicates the maximum and minim-um densitiesobtained from The following examples illustrate developer formulas usedto obtain an increase in maximum density over that obtained with thesame developer containing no anti-foggant.

Example 6 Grams Hydroquinone 10 Sodium sulfite 16 p-Formaldehyde 4Sodium carbonate 25 Benzotriazole 0.1 Water to 1 liter Example 7 GramsHydroquinone 20 Sodium sulfite 32 p-Formaldehyde 8 Sodium carbonate 50Benzotriazole 0.8 Water to 1 liter Example 8 Grams Hydroquinone 30Sodium sulfite 48 p-Formaldehyde 12 Sodium carbonate .75 Benzotriazole1.2 Water to 1 liter Example 9 Grams Hydroquinone 30 Sodium sulfite 48p-Formaldehyde 12 Benzotriazole 2.4 Water to 1 liter Example 10 v GramsHydroquinone 30 Sodium sulfite e- 24 p-Formaldehyde 6 Benzotriazole 2.5Water to 1 liter Example 11 Grams Hydroquinone -1 30 Monomethyl p-aminophenol sulfate 0.25 Sodium sulfite 50 p-Formaldehyde 12.5 Sodiumhydroxide 6 Benzotriazole 2.5

Water to 1 liter When alkalis such as sodium hydroxide or sodiumcarbonate in large amounts are added to these developers in order toincrease the pH for the purpose of decreasing development time, thedevelopers exhibit a tendency to produce lower maximum density. andhigher minimum density. This tendency may be overcome by incorporatingsmall amounts of agents such as p-phenylenedi amine or N-methyl-p-aminophenol sulfate, hydroxy hydroquinone or hydrox hydroquinone acetate, inthe developers. Example 11 illustrates a developing solution of thistype to which sodium hydroxide and N-methyl-p-amino phenol sulfate havebeen added. A disadvantage of the developers compounded with smallamounts of diamino phenylenes or amino phenols is that the amino groupsof these compounds apparently react slowly with the formaldehyde of thedeveloper, yielding Schifis bases; therefore these developers are mosteffective when used within a few hours after preparation. a

The amounts of the diamino 'phenylenes and amino phenols which haveproved most satisfactory for incorporation in the developers are of theorder of 0.12 to 0.5 g. per liter of developing solution. In the case ofhydroxy hydroquinone and hydroxy hydroquinone triacetate, amounts whichhave proved most efiicacious are of the order of 0.12 to 0.4 g. perliter of developer.

Not all compounds which ma exhibit antifoggant properties are useful inincreasing the maximum density of the reversal image obtained withinternal latent image emulsions. For example, fi-phenylindole,1,3-dimethylindole, phenyl mercapto tetrazole, 2-methylbenzoxazoleethiodide, Z-methylbenzothiazole, metho-p-toluene sulfonate,thiobarbituric acid, 2,6-dimethylquinoline, 2,6-dimethyl quinoliniumethiodide and sulfonamidobenzotriazole decreased the maximum densityover that obtained with developers not containing these agents. Othercompounds such as 3,5-dimethyl pyrazole, barbituric acid and2-fl-acetanilido vinyl benzoxazole ethiodide produced no effect oneither the maximum or the minimum densities obtained.

From the foregoing examples and description, it will be seen that thenovel and useful features of my invention consist in the discovery andapplication of certain anti-foggant or heterocyclic nitrogen compoundsin developers for the production of direct positive photographic imagesof improved contrast and extended density scale (increased shoulderdensity) by development in low sulfite or formaldehyde bisulfite typedevelopers. It is to be understood that the scope of my invention is notto be limited by the specific concentrations or formulations given in.the above examples.

Observation of the developing solution containing benzotriazole beforeand after development revealed the fact that it was greatly discoloredduring development. It is thought that intermediate oxidation productsof hydroquinone increased the production of aerial fog. In the developercontaining benzotriazole, it appears from this observation that the rateof production of intermediate oxidation products from hydroquinone isincreased and that this results in an increase in aerial fog production.This property of the compounds described herein would seem to be quiteindependent of their normal anti-foggant properties which ma existsimultaneouslywith the accelerating action on the aerial fog as the toecharacteristics of the above examples reveal.

I claim:

1. The method of obtaining a direct positive image in a silver halideemulsion layer, which comprises exposing to light rays to which theemulsion is sensitive, a silver halide emulsion layer a test portion ofwhich upon exposure to a light intensity scale for a fixed time between/100 and 1 second and development for 3 minutes at C. in the followinginternal type developer:

Water to 1 liter gives a maximum density at least 5 times the maximumdensity obtained when the equally exposed silver halide emulsion isdeveloped for 4 minutes at 20 C. in the following surface developer (I):

Water to 1 liter and developing the unexposed portion of said emulsionlayer in an aerial fogging developer with access of oxygen, andcontaining a heterocyclic, nitrogen-containing ring compound whichincreases the maximum density of the positive image obtained in saidaerial fogging developer, said heterocyclic compound being selected fromthe group consisting of benzotriazole, methyl benzotriazole, ethylbenzotriazole, l-ethyl oxindole, 5-nitroindazole, 6-nitrobenzimidazole,histidine, ethyl benzoxazole, N-ethyl pyrrole, 2,5-dimethylpyrrole,2,4-dimethyl 5 carbethoxypyrrole, 2,3-dimethyl quinoxaline,2-thio-2,4(3,5)- thiazoledione, 2,4,6-tri-isopropylamino S triazine,2,4-dimethylamino-6-chloro S triazine, 2,4-di (5 methoxyethylamino) 6chloro S- triazine, 2,4,6-tri-n-butylamino S triazine, 1-carboxymethyl-3-phenyl-2 thiohydantoin, 1,4-diphenyl-3-anilino-5-phenylimino, and 1,2,4-triazoline.

2. The method of obtaining a directpositive image in a silver halideemulsion layer, which comprises exposing to light rays to which theemulsion is sensitive, a silver halide emulsion layer a test portion ofwhich upon exposure to a light intensity scale for a fixed time betweenand 1 second and development for 3 minutes at 20 C. in the followinginternal type developer:

Water to 1 liter gives a maximum density at least 5 times the maximumdensity obtained when the equally exposed silver halide emulsion isdeveloped for 4 minutes at 20 C. in the following surface developer (I):

Grams p-Hydroxyphenylglycine 10 Sodium carbonate 100 Water to 1 literand developing the unexposed portion of said emulsion layer in an aerialfogging developer with access of oxygen, and containing benzotriazole,which increases the maximum density of the positive image obtained insaid aerial fogging developer.

3. The method of obtaining a direct positive image in a silver halideemulsion layer, which comprises exposing to light rays to which theemulsion is Sensitive, a silver halide emulsion layer a test portion ofwhich upon exposure to a light intensity scale for a fixed time between/100 and 1 second and development for 3 minutes at 20 C. in thefollowing internal type developer:

Grams Hydroquinone 15 Monomethyl-p-aminophenol sulfate 15 Anhydroussodium sulfite 50 Potassium bromide 10 Sodium hydroxide 25 Sodiumthiosulfate 20 Water to 1 liter gives a maximum density at least timesthe maximum density obtained when the equally exposed silver halideemulsion is developed for 4 minutes at 20 C. in the following surfacedeveloper (I):

Grams p-Hydroxyphenylglycine Sodium carbonate 100 Water to 1 liter anddeveloping the unexposed portion of said emulsion layer in an aerialfogging developer with access of oxygen, and containing 5-nitroindazole,which increases the maximum density of the positive image obtained insaid aerial fogging developer.

4. The method'of obtaining a direct positive image in a silver halideemulsion layer, which comprises exposing to light rays to which theemulsion is sensitive, a silver halide emulsion layer a test portion ofwhich upon exposure to a light intensity scale for a fixed time between/100 and 1 second and development for 3 minutes at 20 C. in thefollowing internal type developer;

Grams Hydroquinone Monomethyl-p-aminophenol sulfate 15 Anhydrous sodiumsulfite 50 Potassium bromide 10 Sodium hydroxide 25 Sodium thiosulfateWater to 1 liter 10 gives a maximum density at least 5 times the maximumdensity obtained when the equally exposed silver halide emulsion isdeveloped for 4 minutes at 20 C. in the following surface developer (I):

Grams p-Hydroxyphenylglycine 10 Sodium carbonate 100 Water to 1 literand developing the unexposed portion of said emulsion layer in an aerialfogging developer with access of oxygen, and containingS-nitrobenzimidazole, which increases the maximum density of thepositive image obtained in said aerial fogging developer.

ROBERT ELIOT STAUFFER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,271,229 Peterson et al Jan. 27,1942 2,384,593 Bean Sept. 11, 1945 2,401,051 Crouse et a1. May 28, 1946OTHER REFERENCES Wall: Photographic Emulsions, publ. 1929 by Amer. Phot.Publ. 00., Boston: pages 52 and 53.

1. THE METHOD OF OBTAINING A DIRECT POSITIVE IMAGE IN A SILVER HALIDEEMULSION LAYER, WHICH THE COMPRISES EXPOSING TO LIGHT RAYS TO WHICH THEEMULSION IS SENSITIVE, A SILVER HALIDE EMULSION LAYER A TEST PORTION OFWHICH UPON EXPOSURE TO A LIGHT INTENSITY SCALE FOR A FIXED TIME BETWEEN1/100 AND 1 SECOND AND DEVELOPMENT FOR 3 MINUTES AT 20*C. IN THEFOLLOWING INTERNAL TYPE DEVELOPER: